1. Field of the Invention
The invention relates to a process and a device for making hollow billets into tubes in several operations.
2. Background Art
A hollow billet, as is generally known, means the hollow cylindrical intermediate product in the production of tubes. For the production of the hollow billet, usually-rolled-round shaped steel or continuous casting is pierced by a mandrel in a rotary piercing mill. The hollow billet is then roughed down in a breaking-down rolling mill for further elongating and leveling of the wall thickness. The roughing down generally takes place in two operations, that is, so-called passes. In each of the two passes, the hollow billet is advanced over a piercer placed on the front end of a piercer rod by a pair of working rolls, after which the piercer is removed and the hollow billet is retracted by return rolls. In the second pass a piercer somewhat greater in size than the first is used. Then, the inside wall of the hollow billet is smoothed in a reeling mill.
Before the first pass a descaling agent, to which a lubricant is added, is applied in the hollow billet. This takes place, for example, by means of the device described in European Published Patent Application No. 250,881, which by means of a sliding unit is brought up to the hollow billet hollow space and centered, after which an air current, laden with the descaling agent, is conducted into the hollow billet hollow space by the device. After the amount of air, laden with the descaling agent, has flowed through the hollow space, the device is retracted by means of the sliding unit. After the end of the reaction time necessary for the descaling, the first pass then takes place.
Before the second pass, a lubricant powder or granulate is applied in each case in the hollow billet. Since the two passes are to be performed successively with as little interruption as possible (interrupted only by putting the second piercer on the piercer rod), only a short time remains for application of the lubricant. For this reason, in the prior art, it is thrown into the front end of the hollow billet by a worker by means of a shovel. The same also happens in the prior art before smoothing in the reeling mill: a worker throws a lubricant into the hollow billet by means of a shovel.
The known application of the lubricant is disadvantageous for several reasons. An operator is used for that purpose alone or the process is delayed if the operator responsible for putting on the piercer must also apply the lubricant. (In the usual process times the worker must reapply lubricant about every 10 seconds, so that practically no time remains for other work. Throwing in the lubricant result in a dust cloud polluting the environment, harmful to the operator's health. Lubrication is uneven and great amounts of lubricant are consumed, since throwing the lubricant results in an adhesion of the lubricant in the front, lower part of the hollow billet inside wall, while the upper, back areas of the hollow billet inside wall are not sufficiently or only insufficiently supplied with lubricant.